The Preston Pressure PS-525 is a portable digital pitot-static test set used for testing and calibrating aircraft altimeters, airspeed indicators, and pitot-static systems. It is designed for general aviation (non-RVSM) applications and provides a compact, all-in-one solution for avionics maintenance and pitot-static leak testing.

The unit is fully self-contained, operating on either external 24V DC power or internal rechargeable batteries, allowing completely portable operation in hangars or remote environments. It uses internal pumps and reservoir systems to generate controlled pressure and vacuum for simulating altitude and airspeed conditions during instrument testing.

The PS-525 also includes an integrated encoder reader, capable of interpreting gray code and RS-232 outputs, making it useful for checking altitude encoders and transponder-related data during maintenance.

It is widely used in avionics shops as a modern replacement for older mechanical pitot-static test boxes due to its digital display, reduced maintenance, and improved portability.

Key features include:

Preston Pressure model: PS-525
Portable digital pitot-static tester
Designed for aircraft altimeter and airspeed testing
Supports non-RVSM systems
Internal pressure and vacuum pump system
Powered by 24V DC or internal rechargeable batteries
Integrated encoder reader (gray code + RS-232)
Altitude simulation up to ~35,000 ft range
Airspeed simulation up to ~650 knots
Leak test and VSI simulation functions
Lightweight portable design (~20 lb / 9 kg) 
Used in aircraft maintenance and avionics calibration shops
Includes hoses, power supply, and calibration certificate (standard package)